For the past two decades, titanium alloy has been widely used in the golf club industry because it has excellent corrosion resistance and high specific strength (strength and density ratio. Titanium alloy currently accounts for about 30 to 40 percent of the overall market.
Early in the selection of titanium alloy materials, pure titanium (G4) and Ti-6A1-4V were mainly chose because they have the character of making the golf club head (Driver) from the original volume using an iron-based alloy of 250˜270 cc raised to 320˜350 cc. With increased design requirements for the club head, a high-intensity β-type titanium alloy started to be used about ten years ago, such as 15-3-3-3, 10-2-3, 2041 titanium alloys. The main feature is allowing the volume of the golf club head to be raised to 400˜450 cc.
With the enhancement and stability in process technology, the volume of the current titanium golf club head (Driver) has reached 450˜470 cc, complying with the international norm of 460 cc. In addition, considering the cost of raw materials, the golf club head industry also uses molybdenum and/or chromium containing alloys, such as: 4.5-3-1-1, SP700, BT14, 5-1-1-1, Ti735, etc. Moreover, considering the low Young's modulus and shock/vibration absorption, high molybdenum alloys, such as 15-3 and 15-5-3, have also been developed.
The golf club head can be broadly divided into three categories: wood, iron, and putter, summarized as follows:
1. Wood head: It is used for the drive, and the requirement is to hit the ball a long, straight distance. Because titanium alloy has a high specific strength and low proportions, the sweet area is larger, thereby maintaining the stability of direction. Wood clubs are generally formed with stainless steel, but a combination of different materials for producing the composite wood head can create a counterweight to achieve the best results.
2. Irons head: It is used for hitting the ball to the greens or scheduled locations, and the requirements are accuracy and stable flight distance. The material is mainly stainless steel. Regarding the material of the iron head, the major development are: an elongation of 20˜30% and a high strength (over 150 kips/in2), or a strength of 100˜120 kips/in2 (psi) and a high elongation (over 30%).
3. Putter: The putter is used to push the ball into the hole on the greens, which is mainly used to control the direction of the ball and focuses on balance. This means preventing the striking plate from rotating while maintain the putter club head and the pipe. Recently, computer numerical control (CNC) has been used to process the club head in order to maintain the position of the designed barycenter and the uniformity of the club head.
In recent years, due to the limited volume of the club head, in order to increase the design flexibility of the club head in the weight distribution, a titanium alloy with a density lower than that of Ti-6Al-4V (US 2006/0045789, 4.42˜4.48 g/cm3) has been thus developed, which is an important development for the golf club industry. For example, the Ti-8Al-1V-1Mo alloy began mass production in 2009 (cast density of 4.30˜4.36 g/cm3).
Titanium alloy is an excellent material for the golf club head, but the design of the golf club head has moved toward the limit in recent years, without respect to thickness or shape. For example, the thickness of the striking face has decreased from 2.5 mm˜3.6 mm to 2.1 mm˜2.5 mm, and the thickness of the top cap has decreased from 1.0 mm˜1.2 mm to 0.6 mm˜0.8 mm, so that the result of the golf club head in the shelling test is between 200 and 4000 hits under the design conditions, and is much lower than the result of past experience, which is 5000-14000 hits. Regarding the general shelling test, the criteria is more than 3000 hits at a certain pace, so the property of the golf club head is disposed on the edge of the criteria. In addition, according to past analysis, if the process was once carried out between 800 and 950° C., the microstructure of the golf club heads made of 8-1-1 or 6-4 titanium alloys would cause an interphase to easily be formed between the α-phase/β-phase interfacial interphase, and induce the formation of microcracks; this is the main reason why the result in the shelling test is between 200 and 4000 hits.
However, due to the requirements of a large scaled golf club head and a variety of customizations, it is necessary to develop an alloy with a low density and high extension, but still maintaining mechanical strength in order to improve design flexibility.
Therefore, it is necessary to develop a golf club head and a low density alloy thereof to solve the problems existing in the conventional technology, as described above.